1. Technical Field
The invention relates generally to energy-based systems, and in particular to a method and system for adaptive regenerative energy control.
2. Discussion of the Background Art
It is known in many applications, including self-propelled vehicle applications, to employ a dynamoelectric machine in a first mode as a motor in order to provide propulsion torque. In such applications, it is also known to reconfigure the dynamoelectric machine in a second mode as a generator, in order to capture and convert some of the potential or kinetic energy associated with the application into output electrical power, a process known as regeneration (“regenerative energy”). Moreover, in such applications, it is also known to provide an energy storage device, such as a battery, to power the dynamoelectric machine when operated as a motor, and to receive the regenerative energy when the dynamoelectric machine is operated as a generator. In the latter case, the regenerative energy is generally operative to increase the state of charge of the battery, until such battery is “fully” charged. Battery technologies typically used in such applications include nickel metal hydride (NiMH), lead acid (PbA) and nickel cadmium (NiCd) technologies.
One aspect of the above systems that involves tradeoffs or compromises pertains to the charging (or recharging) regimens. Specifically, while it would generally be desirable to charge the battery to its highest possible state of charge (which in turn would provide the greatest range or longest duration use for the application running off the battery), such an approach is often tempered to allow for acceptance of regenerative energy. Thus, a pair of known charging (or recharging) regimens involves (i) recharging the battery to 100% of its maximum state of charge or (ii) selecting some predetermined backoff position in advance.
It is noteworthy that the above battery technologies are somewhat tolerant of overcharging, at least up to a point, wherein input of regenerative energy above and beyond the “fully” charged level is dissipated as heat. Such a situation may occur when the battery, as fully charged, immediately receives a large level of regenerative energy. However, some known battery systems have thermal protection, which will disable the battery system when a maximum, threshold temperature is reached.
The other approach mentioned above taken in the art for battery charging regimens, which involves specifying a fixed, predetermined headroom to allow for acceptance of regenerative energy inputs (e.g., to minimize or eliminate the chance of overcharging), also has shortcomings. For example, in such approaches, a recharge level of a predetermined percent less than 100% may be specified in advance of the actual use. This fixed “headroom” allows for some level of regenerative energy to be applied to the battery system without overcharging. For applications where the power usage and regenerative energy input are relatively known in advance, this approach may provide satisfactory results. However, where the usage and regeneration patterns are expected to be (and are) unpredictable and variable, the fixed headroom approach is inflexible and inefficient. In most cases this fixed “headroom” is conservatively set (i.e., with the worst case in mind—so as to accept the largest possible regenerative energy inputs). This approach thus represents an inherent compromise, inasmuch as the total range or duration of use running off the battery would be decreased relative to a battery charged to 100% of its maximum state of charge.
Another battery technology in addition to the above mentioned types is known, and involves lithium chemistries, as seen by reference to U.S. Pat. No. 6,063,519 to Barker et al. One characteristic, however, of lithium chemistry batteries is that it has less tolerance to overcharging than the other battery technologies referred to above. That is, in many instances, the additional voltage, and in part, heat due to overcharging may seriously impair or damage the battery. Accordingly, the known charging regimen where the battery is charged to 100% is realistically unavailable in the circumstances described above, since the possibility of receiving regenerative energy when the battery is fully charged could have catastrophic results.
There is therefore a need for a charging regimen that minimizes or eliminates one or more of the above-identified problems.